Concentric opposed cam actuator

ABSTRACT

An example device may include a rounded outer incline ramp and a rounded inner incline ramp surrounding a central axis. The rounded inner incline ramp and the rounded outer incline ramp may be inversely aligned relative to the central axis. The device may also include a piston carrier oriented in a direction parallel to the central axis. The piston carrier may include a first piston including a first roller positioned on the two ramps at a first point, where the first piston is configured to act on the two ramps in a direction parallel to the central axis. The piston carrier may also include a second piston including a second roller positioned on the two ramps at a second point opposite the first point, where the second piston is configured to act on the two ramps in a direction parallel to the central axis.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/490,382, filed on Sep. 18, 2014, and entitled “ConcentricOpposed Cam Actuator,” which claims priority to U.S. Provisional patentapplication Ser. No. 62/041,519, filed on Aug. 25, 2014, and entitled“Concentric Opposed Cam Actuator,” each of which is herein incorporatedby reference as if fully set forth in this description.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

A robotic device includes a mechanical agent, usually anelectro-mechanical machine that is guided by a computer program orelectronic circuitry. Robots can be autonomous or semi-autonomous andrange from humanoid designs, to large industrial designs with jointedarms and end effectors to perform specialized tasks.

Such robotic devices may include several joints configured to enable therobotic device to perform a variety of functions and movements. Forexample, a humanoid robotic device may include hip joints, ankle joints,and/or wrist joints. In some example operations, such joints of arobotic device may use rotational motion to perform desired functions.Motions of robotic joints may be controlled by actuators, which may beoperated by a source of energy such as electric current or hydraulicfluid pressure. The actuators may convert the energy into motion, suchas to rotate a joint of a robotic device.

SUMMARY

The present application discloses embodiments that relate to aconcentric opposed cam actuator. In one example, an actuator may includean outer end cam and an inner end cam nested inside the outer end cam.The two end cams may be shaped as rounded incline ramps surrounding acentral axis and may be inversely aligned relative to the central axisto allow a piston carrier to act on the two ramps. The actuator mayadditionally include a piston carrier with two antagonistic pistonsoffset from the central axis. The first piston may contain a roller thatacts on the two ramps at a first point, and the second piston maycontain a roller that acts on the two ramps at a second point oppositethe first point. Linear actuation of one of the pistons toward the endcams may cause rotation of at least one of the end cams, and may alsocause linear motion of the other piston in a direction away from the endcams.

In one example, a device is disclosed. The device may include a roundedouter incline ramp surrounding a central axis. The device may furtherinclude a rounded inner incline ramp surrounding the central axis with asmaller radius than the rounded outer incline ramp, where the roundedinner incline ramp and the rounded outer incline ramp are inverselyaligned relative to the central axis. The device may additionallyinclude a piston carrier oriented in a direction parallel to the centralaxis. The piston carrier may include a first piston including a firstroller positioned on the rounded outer incline ramp and the roundedinner incline ramp at a first point, where the first piston isconfigured to act on the rounded outer incline ramp and the roundedinner incline ramp in a direction parallel to the central axis. Thepiston carrier may further include a second piston including a secondroller positioned on the rounded outer incline ramp and the roundedinner incline ramp at a second point opposite the first point, where thesecond piston is configured to act on the rounded outer incline ramp andthe rounded inner incline ramp in a direction parallel to the centralaxis.

In another aspect, a robotic system is disclosed. The robotic system mayinclude at least one rotational joint and at least one actuatorconfigured to enable rotation of the at least one rotational joint. Theat least one actuator may include a rounded outer incline rampsurrounding a central axis. The at least one actuator may furtherinclude a rounded inner incline ramp surrounding the central axis with asmaller radius than the rounded outer incline ramp, where the roundedinner incline ramp and the rounded outer incline ramp are inverselyaligned relative to the central axis. The at least one actuator mayadditionally include a piston carrier oriented in a direction parallelto the central axis. The piston carrier may include a first pistonincluding a first roller positioned on the rounded outer incline rampand the rounded inner incline ramp at a first point, where the firstpiston is configured to act on the rounded outer incline ramp and therounded inner incline ramp in a direction parallel to the central axis.The piston carrier may further include a second piston including asecond roller positioned on the rounded outer incline ramp and therounded inner incline ramp at a second point opposite the first point,where the second piston is configured to act on the rounded outerincline ramp and the rounded inner incline ramp in a direction parallelto the central axis.

In yet another aspect, a method is disclosed. The method may includedetermining a grounded component from a group of three components toenable rotation of two ungrounded components from the group about acentral axis, where the group comprises (1) a rounded outer incline rampsurrounding the central axis, (2) a rounded inner incline rampsurrounding the central axis and inversely aligned from the roundedouter incline ramp, and (3) a piston carrier oriented in a directionparallel to the central axis. The method may further include causing thegrounded component to become fixed from rotation about the central axis.The method may additionally include driving a first piston of the pistoncarrier toward the rounded outer incline ramp and the rounded innerincline ramp to produce rotations of the two ungrounded components andto force a second piston from the piston carrier in a direction awayfrom the rounded outer incline ramp and the rounded inner incline ramp.

In a further aspect, a system may include means for determining agrounded component from a group of three components to enable rotationof two ungrounded components from the group about a central axis, wherethe group comprises (1) a rounded outer incline ramp surrounding thecentral axis, (2) a rounded inner incline ramp surrounding the centralaxis and inversely aligned from the rounded outer incline ramp, and (3)a piston carrier oriented in a direction parallel to the central axis.The system may further include means for causing the grounded componentto become fixed from rotation about the central axis. The system mayadditionally include means for driving a first piston of the pistoncarrier toward the rounded outer incline ramp and the rounded innerincline ramp to produce rotations of the two ungrounded components andto force a second piston from the piston carrier in a direction awayfrom the rounded outer incline ramp and the rounded inner incline ramp.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a functional block diagram illustrating a robotic device,according to an example embodiment.

FIG. 2A illustrates components of an actuator, according to an exampleembodiment.

FIG. 2B illustrates a side view of an actuator, according to an exampleembodiment.

FIG. 2C illustrates a cross-sectional view of an actuator, according toan example embodiment.

FIGS. 3A-3C illustrates examples of concentric nested cams, inaccordance with at least some embodiments described herein.

FIG. 4 illustrates a robotic arm, according to an example embodiment.

FIG. 5 depicts a computer-readable medium, according to an exampleembodiment.

FIG. 6 is a flowchart illustrating an example method, according to anexample embodiment.

DETAILED DESCRIPTION

Example methods and systems are described herein. It should beunderstood that the words “example,” “exemplary,” and “illustrative” areused herein to mean “serving as an example, instance, or illustration.”Any embodiment or feature described herein as being an “example,” being“exemplary,” or being “illustrative” is not necessarily to be construedas preferred or advantageous over other embodiments or features. Theexample embodiments described herein are not meant to be limiting. Itwill be readily understood that the aspects of the present disclosure,as generally described herein, and illustrated in the figures, can bearranged, substituted, combined, separated, and designed in a widevariety of different configurations, all of which are contemplatedherein.

Robotic devices may include several joints configured to enable therobotic device to perform a variety of functions and movements. Forexample, a robotic device may include hip joints, ankle joints, and/orwrist joints. In some example operations, such joints of a roboticdevice may use rotational motion to perform desired functions. Motionsof robotic joints may be controlled by actuators, which may be operatedby a source of energy such as electric current or hydraulic fluidpressure. In some examples, an actuator may convert linear motion intorotational motion, such as to rotate a joint of a robotic device.

More specifically, a linear-to-rotary transmission actuator may be usedto convert linear motion from linearly actuated pistons into rotarymotion to create rotary reciprocating motion for a twist joint of arobot, such as a forearm. A linear-to-rotary actuator may use twoantagonistic pistons that act on a helix-shaped end cam capable ofrotation. As one piston pushes down, the end cam may rotate, which maycause the second piston to get pushed back up. To rotate in the otherdirection, the second piston may be driven to push down on the end cam,causing the end cam to rotate in the other direction and also causingthe first piston to get pushed back up. An actuator with antagonisticpistons and a single helix-shaped end cam may be limited to a range ofless than 180 degrees of rotational motion because each piston may onlybe able to act on half of the surface of the end cam.

Example embodiments may use two concentric, nested cams to provide agreater range of rotational motion. More specifically, a first end cammay be shaped as a circular outer incline ramp surrounding a centralaxis. A second end cam may be shaped as a circular inner incline rampthat is nested inside the outer end cam and aligned opposite the outerend cam. Aligning the outer end cam and the inner end cam opposite eachother may cause the outer end cam and the inner end cam to cross at twopoints orthogonal to the central axis (e.g., to have the same height orroughly the same height as measured in a direction along the centralaxis).

Additionally, an actuator may include a piston carrier containing twoantagonistic pistons which each have rollers that act on both the outerend cam and the inner end cam. The first piston may act on both end camsat the first point where the outer end cam and the inner end cam cross.The second piston may act on both end cams at the second point where theouter cam and the inner cam cross. Furthermore, the piston carrieritself may also be capable of rotation about the central axis.

The actuator therefore may include three concentric bodies (e.g., thepiston carrier and the two end cams) that each can rotate about acollinear axis. Within examples, any one of the three concentric bodiescan be used as a ground and held fixed from rotation while the other twobodies are allowed to rotate.

To provide a range of rotational motion greater than 180 degrees, one ofthe end cams may be held fixed. For instance, the inner end cam may befixed from rotating. As a piston from the piston carrier pushes down onthe two end cam surfaces, the piston carrier may then rotate based onthe helix angle of the inner cam. The roller at the end of the pistonmay also transfer motion to the outer earn through the helix angle ofthe outer cam. This rotation on top of rotation based on the helixangles of the two cams may produce a gearing effect to increase therotational motion of the outer cam. The helix pitch of a cam depends onboth the cam radius and the helix angle. If the helix pitch of the twocam surfaces is the same, the rotational motion of the outer earn may bedoubled with half the torque output. In other examples, the two camsurfaces may have a different helix pitch to create different gearratios.

Additionally, the rotational motion may be produced with low frictionand no backlash. To enable the mechanism to have zero backlash, theretracting linear body may be provided with a minor pre-load against thecam surfaces. For instance, in an example hydraulic variant, this may beaccomplished by creating an effective ‘H-bridge’ between the two fluidchambers behind the pistons. When one piston is actuated (i.e.,extended), its fluid chamber is connected to the supply pressure (highpressure), while the retracting piston's fluid chamber is connected tothe return line (low pressure), thus flowing back to the reservoir asthe piston retracts. The return pressure acts as a spring to keep theretracting piston in contact with the cams. When the ‘H-bridge’ istoggled and the retracting piston's fluid chamber is connected to thesupply pressure (high pressure), the actuator moves in the otherdirection and without backlash because the retracting piston waspreviously in contact. The hydraulic analogue of the ‘H-bridge’ is aservo valve.

In further examples, the transmission may be used as a type ofdifferential. For instance, the piston carrier may be chosen as theground, and fixed from rotating. As a piston from the piston carrierpushes down, the outer end cam and the inner end cam may be caused torotate in opposite directions as the roller of the piston moves down theramps of both cams. Linear motion of the piston may therefore betransferred to rotational motion of both end cams. Depending on thehelix angles of the two end cams, a different angular velocity may beproduced for each of the two end cams.

In further examples, the ramps of one or both cams may undulate ratherthan having a straight helix slope. This may allow the transmission tohave different gear ratios at different points of the cams. At a shallowhelix angle, most of the piston force may be directed to pushing on thecam surface, rather than causing rotation. At a steep helix angle, mostof the force may produce torque that rotates the cam. This type ofdesign may be useful for joints (e.g., of a robot) where asymmetry injoint strength is desirable (e.g., stronger at some points of motion andfaster at other points of motion). In additional examples, this type ofnon-linear transmission may also help to optimize the overall packaginglength. In particular, a steeper cam angle implies a taller assembly(e.g., axially).

It should be understood that the above examples are provided forillustrative purposes, and should not be construed as limiting. As such,example systems and methods may additionally or alternatively includeother features or include fewer features, without departing from thescope of the invention.

Referring now to the figures, FIG. 1 illustrates a functional blockdiagram illustrating a robotic device 100, according to an exampleembodiment. The robotic device 100 may include various subsystems suchas a mechanical system 120, a sensing system 130, a control system 140,as well as a power supply 150. The robotic device 100 may include moreor fewer subsystems and each subsystem could include multiple elements.Further, each of the subsystems and elements of robotic device 100 couldbe interconnected. Thus, one or more of the described functions of therobotic device 100 may be divided up into additional functional orphysical components, or combined into fewer functional or physicalcomponents. In some further examples, additional functional and/orphysical components may be added to the examples illustrated by FIG. 1.

The mechanical system 120 may include several components, including abody 102, one or more robotic legs 104, and one or more robotic feet 106coupled to the one or more robotic legs 104. The mechanical system 120may also include one or more robotic joints 107, configured to enablethe robotic device to perform a variety of functions and movements, asdiscussed in more detail below. The mechanical system 120 mayadditionally include a motor 108, which may be an electric motor poweredby electrical power, or may be powered by a number of different energysources, such as a gas-based fuel or solar power. Additionally, motor108 may be configured to receive power from power supply 150. The powersupply 150 may provide power to various components of robotic device 100and could represent, for example, a rechargeable lithium-ion orlead-acid battery. In an example embodiment, one or more banks of suchbatteries could be configured to provide electrical power. Other powersupply materials and types are also possible.

The sensing system 130 may determine information about the environmentthat can be used by control system 140 (e.g., a computing device runningmotion planning software). The control system 140 could be located onthe robotic device 100 or could be in remote communication with therobotic device 100. In one particular example, the sensing system 130may use one or more body-mounted sensors 110 attached to the body 102 ofthe robotic device 100, which may be 2D sensors and/or 3D depth sensorsthat sense information about the environment as the robotic device 100moves. For example, the body-mounted sensors 110 may determine adistance between the body 102 of the robotic device 100 and the groundsurface on which the robotic device 100 operates. In further examples,one or more robotic leg sensors 112 may be located on the robotic legs104 of the robotic device 100. The robotic leg sensors 112 may becontact sensors configured to alert the robotic device when the roboticlegs 104 are in contact with the ground surface. In another example, therobotic legs 104 may be coupled to robotic feet 106 that contact theground surface. In such a case, the robotic device 100 may include oneor more robotic feet sensors 114 positioned on the robotic feet 106 ofthe robotic device 100. The robotic feet sensors 114 may be contactsensors configured to alert the robotic device 100 when the robotic feet106 are in contact with the ground surface.

The sensing system 130 may further include an inertial measurement unit(IMU) 116. In an illustrative embodiment, IMU 116 may include both anaccelerometer and a gyroscope, which may be used together to determinethe orientation, position, and/or velocity of the robotic device 100. Inparticular, the accelerometer can measure the orientation of the roboticdevice 100 with respect to gravity, while the gyroscope measures therate of rotation around an axis. IMUs are commercially available inlow-cost, low-power packages. For instance, an IMU 116 may take the formof or include a miniaturized MicroElectroMechanical System (MEMS) or aNanoElectroMechanical System (NEMS). Other types of IMUs may also beutilized. The IMU 116 may include other sensors, in addition toaccelerometers and gyroscopes, which may help to better determineposition and/or help to increase autonomy of the robotic device 100. Twoexamples of such sensors are magnetometers and pressure sensors. Otherexamples are also possible.

The sensing system may further include one or more load cells 117. Loadcells 117 may be provided at all of the robotic joints 107 of therobotic device 100, or at selected joints such as an elbow joint, forexample. Example load cells 117 may include a multi-axis load cell thatincludes strain gauges on multiple surfaces to sense forces alongmultiple axes. Urethane (or other rubber, plastic, epoxy material) maybe included surrounding the load cell to enable an applied force to besensed by the strain gauges.

An example load cell 117 may be internal to an actuator of the roboticjoint 107 and coupled between the actuator 102 and the robotic joint107, provided on the actuator, or provided on the robotic joint 107. Theload cell 117 may further be a component internal of the robotic joint107. The load cell 117 may include a transducer to detect and convert anapplied force to the robotic manipulator into an electrical signal. Forexample, a force being sensed deforms a strain gauge of the load cell117, and the strain gauge measures the deformation (strain) as anelectrical signal because the strain changes an effective electricalresistance of the gauge. The load cell 116 may include four straingauges in a Wheatstone bridge configuration, one strain gauge in aquarter-bridge configuration, or two strain gauges in a half-bridgeconfiguration. The electrical signal output may be in the order of a fewmillivolts and may be amplified as well.

Many or all of the functions of the robotic device 100 could becontrolled by control system 140. Control system 140 may include atleast one processor 118 (which could include at least onemicroprocessor) that executes instructions 122 stored in anon-transitory computer readable medium, such as the memory 124. Thecontrol system 140 may also represent a plurality of computing devicesthat may serve to control individual components or subsystems of therobotic device 100 in a distributed fashion.

In some embodiments, memory 124 may contain instructions 122 (e.g.,program logic) executable by the processor 118 to execute variousfunctions of robotic device 100, including those described below. Memory124 may contain additional instructions as well, including instructionsto transmit data to, receive data from, interact with, and/or controlone or more of the mechanical system 120, the sensor system 130, and/orthe control system 140.

As described above, a robotic device may include several jointsconfigured to enable the robotic device to perform a variety offunctions and movements. For example, a humanoid robotic device mayinclude hip joints, ankle joints, and/or wrist joints. Such roboticjoints may use a linear-to-rotary transmission actuator to producerotational motion. FIG. 2A illustrates components of a device forconverting linear motion to rotational motion, according to an exampleembodiment.

More specifically, the actuator may include an outer end cam 202 that isoriented around a central axis that may run through a center line of thedevice. The outer end cam 202 may be shaped as a rounded incline ramp.For instance, the outer end cam 202 may include a first semicircularportion that extends from a lowest point to a highest point, and asecond semicircular portion opposite the first semicircular portion. Theouter end cam 202 may contain a top surface on which a roller can bearwith minimal friction. In some examples, the two semicircular portionsmay have the same shape and incline angle. In other examples, the shapeor angle may be different between the two semicircular portions. Otherrounded shapes may be used for the ramp shape as well (e.g., ovals).

The actuator may also include an inner end cam 204 with a smaller radiusthan the outer end cam 202. The inner end cam 204 may also be shaped asa rounded incline ramp. For instance, the inner end cam 204 may includea first semicircular portion that extends from a lowest point to ahighest point, and a second semicircular portion opposite the firstsemicircular portion. In some examples, the inner end cam 204 may havethe same relative shape and/or incline angle as the outer end cam 202.The inner end cam 204 may be oriented around the same central axis asthe outer end cam 202 such that the inner end cam 204 is nested insideof the outer end cam 202. The inner end cam 202 may also contain a topsurface on which a roller can bear with minimal friction.

Additionally, the inner end cam 204 may be inversely aligned relative tothe outer end cam 202. In some examples, this alignment may allow thetop surfaces of the inner end cam 204 and the outer end cam 202 to crossat a first point and a second point orthogonal to the central axis. Inone example, the inner end cam 204 and the outer end cam 202 may becoupled to allow a range of rotational motion including an alignment inwhich the inner end cam 204 is oriented 180 degrees opposite the outerend cam 202. In such a configuration, the highest point of the outer endcam 202 may be aligned with the lowest point of the inner end cam 204and the lowest point of the outer end cam 202 may be aligned with thehighest point of the inner end cam 204.

The actuator may additionally include a piston carrier 206, which mayalso be oriented to surround the central axis. The piston carrier 206may contain a first piston 208 and a second piston 212 which are offsetfrom the central axis. In some examples, the first piston 208 and secondpiston 212 may be offset from the central axis in opposite directions.The first piston 208 may contain a first roller 210 which bears onsurfaces of the inner end cam 204 and the outer end cam 202 at a firstpoint where the inner end camp 204 and the outer end camp 202 crossrelative to the central axis. Additionally, the second piston 212 maycontain a second roller 214 which bears on surfaces of the inner end cam204 and the outer end cam 202 at a second point where the inner end camp204 and the outer end camp 202 cross relative to the central axis.

In further examples, the rollers 210 and 214 may be cylindrical orspherical in shape, and may fit into the surfaces of the outer end cam202 and the inner end cam 204 such that contact between the rollers 210,214 and swept surfaces on the cams 202, 204 may be maintained through anentire range of motion of the pistons 208, 212. In additional examples,the rollers 210 and 214 may each contain two separate rollers which arecapable of rolling independently of one another. More specifically, theroller 210 may contain an outer roller portion (e.g., an outercylindrical roller) which acts on the surface of outer end cam 202 andan inner roller portion (e.g., an inner cylindrical roller) which actson the surface of inner end cam 204. Similarly, the roller 214 may alsocontain an outer roller portion which acts on the surface of outer endcam 202 and an inner roller portion which acts on the surface of innerend cam 204.

In additional examples, each piston assembly may additionally contain athird roller which may act as a constraint on the piston to keep thepiston from rotating (e.g., twisting about the piston axis) due to theforces imparted from the end cams. In some examples, this additionalroller may be located closest to the central axis and may engage a slotlocated within the piston carrier.

The actuator may further include a cylindrical outer housing 218, whichmay contain the end cams 202, 204 and the piston carrier 206. Thehousing 218 may additionally include a circular bottom cap 220 and athrust bearing stack 216 to enclose the rotating components. The thrustbearing stack 216 may support the piston carrier axially and provide alow friction surface against the piston thrust loads. Furthermore, eachof the outer end cam 202, inner end cam 204, and the piston carrier 206may be coupled to at least one of the housing 218, the bottom cap 220,and the thrust bearing stack 216 such that the outer end cam 202, innerend camp 204, and the piston carrier 206 are constrained from radialmotion.

The actuator may additionally include a connector 222 that may allow forconnection with an additional component (e.g., of a robotic device). Forinstance, the connector may include one or more holes near a top end ofthe actuator which may be configured for coupling the actuator to one ormore additional components. In other examples, the actuator may beconnected to other components at other places or in other ways as wellor instead. For instance, a separate connecter could be attached to abottom end of the actuator to couple the actuator to a component in adifferent relative position.

FIG. 2B shows a side view of an actuator, according to an exampleembodiment. Additionally, FIG. 2C shows a cross-sectional view of theactuator, according to an example embodiment. More specifically, theactuator may contain nested concentric end cams 202 and 204, shaped ascircular incline ramps. The actuator may also contain a piston carrier206, which may be capable of rotation about the same central axis as theend cams 202 and 204. In some examples, one of the three concentricbodies (the outer end cam 202, the inner end cam 204, and the pistoncarrier 206) may be held fixed as a ground, while the other twocomponents are allowed to rotate about the central axis. Linear motionof one of the two pistons from the piston carrier 206 may then causerotation of the two ungrounded components.

For instance, in reference to FIGS. 2B and 2C, a piston 212 from pistoncarrier 206 may be driven towards the end cams 202 and 204. Because theend cams 202, 204 are constrained radially, one or both of the end cams202, 204 may be forced to rotate to accommodate the downward motion ofthe roller 214 (depending on which of the rotational components is usedas a ground). The rotation of one or both of the end cams 202, 204 mayforce the other piston 208 back up into the piston carrier 206 viaroller 210. In one example, as illustrated in FIGS. 2B and 2C, when thepiston 212 is driven as far down as its linear range of motion allows,the other piston 208 (not visible in FIG. 2B) may be driven up to apoint where the piston 208 is fully contained within piston carrier 206.

In one example, the pistons 206, 208 may be activated using hydraulicpressure. Accordingly, in order to drive one of the pistons towards theend cams, pressurized hydraulic fluid may be applied in a chamber behindthe piston. Meanwhile, hydraulic fluid may be allowed to flow at leastunimpeded (and optionally assisted by suction, although suction couldcause cavitation and may add backlash) out of a chamber behind thesecond piston to allow the second piston to be driven in an oppositedirection from the first piston. Similar principles may apply if theactuators are powered by voice coil motors, pneumatics, solenoids orother power sources.

Within examples, any one of the three rotational components (the two endcams and the piston carrier) may be chosen as a grounded component andfixed from rotation. In some examples, an extended range of rotationalmotion beyond 180 degrees may be achieved by fixing one of the end camsto produce a gearing effect.

For instance, in one example, the inner end cam may be fixed fromrotation. Then, when one of the pistons pushes down on the two end cams,the roller of the piston will bear against the grounded inner end cam,causing both the outer end cam and the piston carrier to rotate. Morespecifically, the outer end cam will rotate based on the incline angleof the outer end cam. Additionally, the piston carrier will rotate basedon the incline angle of the inner cam, which will also transfer themotion of the piston carrier to the outer end cam. The net result willbe a gearing effect that causes the outer cam to rotate faster than thepiston carrier. If the pitch of the two end cams (which depends on boththe radii and helix angles of the cams) is the same, the net effect willbe a doubling of rotational motion of the outer end cam with half thetorque output.

The gearing effect may allow the outer end cam to achieve a range ofrotational motion greater than 180 degrees even though each piston mayonly act on a 180 degree semicircular portion of each end cam. Becausethe rollers may take up part of the angular rotation, the totalachievable range of rotational motion of the outer end cam may be lessthan 360 degrees, but still relatively close to 360 degrees (e.g.,approximately 340 degrees).

In some examples, an actuator may be designed with equal pitch for theinner cam and outer cam in order to cause the two rotating bodies torotate with the same angular velocity. In other examples, different gearratios may be obtained by using cam surfaces with different pitch.Accordingly, an actuator with different incline angles for the two camsmay produce different angular velocities for the two rotatingcomponents.

In some examples, the two pistons may have the same diameter in order tocreate a balanced actuator that produces the same amount of torque ineither direction. For instance, the mechanism may be designed to produce100 Newton Meters (Nm) in one rotational direction and 100 Nm in thereverse direction as well. In other examples, the piston diameters maybe different to create an unbalanced actuator. By using differentdiameters, one piston may drive with greater force, which may producegreater torque in one direction than the reverse direction.

In further examples, the piston carrier may be fixed from rotation asthe grounded component. In particular, if the piston carrier is fixedfrom rotation and a piston is driven down towards the inner cam and theouter cam, the piston may force the two end cams to rotate in oppositedirections from each other as the roller of the piston moves down theramps of both end cams. Additionally, if the other piston from thepiston carrier is then driven down towards the end cams, the cams mayagain be forced to rotate in opposite directions by forcing both endcams to reverse their direction of rotation.

In additional examples, the mechanism may act as a differential. Inparticular, the differential action may come from the power transferbetween the three elements. If one rotating component is acted upon byan external entity to either speed or slow its motion, the averagevelocity of the other two components will adapt to conserve the inputpower across the rotating members. In further examples, the mechanismcould also work as a limited slip clutch by creating a torsionalpre-load on one of the members. For instance, the piston carrier may begrounded through a friction member that allows a set torque limit. Whenthis torque limit is exceeded through external force on one of the tworotating cams, the piston carrier may slip and then may rotate freely totransfer power.

In examples where the piston carrier is fixed from rotation and thehelix pitch of the two end cams is the same, the two end cams may rotateat the same speed when one of the pistons from the piston carrier actson the end cams. In other examples, the helix pitch of the two end camsmay be different, which may cause the two end cams to rotate withdifferent angular velocities as one of the pistons is driven toward theend cams.

FIG. 3A shows nested concentric cams, according to an exampleembodiment. More specifically, two nested cams 320 may include an outercam 322 and an inner cam 328. The inner cam 328 may have a smallerradius than the outer cam 322 such that the inner cam fits inside theouter cam 322 (e.g., directly adjacent or with a certain amount of spacein between the two cams). The outer cam 322 may have a lowest point 324opposite a highest point 326. Additionally, the inner cam 328 may alsohave a lowest point 330 opposite a highest point 332. In some examples,the outer cam 322 and the inner cam 328 may have a same relative shapeand incline angle to create the same angular velocity for both cams.

Additionally, the outer cam 322 and the inner cam 328 may be coupled inan orientation that causes the surfaces of the outer cam and inner camto have a same height at two points orthogonal to the central axis. Forinstance, in reference to FIG. 3A, the two end cams may have the sameheight or roughly the same height at a first point 334 and at a secondpoint 336. Accordingly, a first piston with a roller configured to acton both the outer cam 322 and the inner cam 328 may be aligned with thefirst point 334. Additionally, a second piston with a roller configuredto act on both the outer cam 322 and the inner cam 328 may be alignedwith the second point 336.

In other examples, the outer cam and the inner cam may have differenthelix angles to allow for a tradeoff between torque and range of motionfor the actuator. In particular, a shallow angle on one cam will givethe corresponding member a high rotation rate (i.e., more range ofmotion), while a steep angle will produce less rotation, but contributeto a higher overall torque. The combination of the cam angles as well asradii defines the mechanical advantage and thus the torque for thesystem. For instance, FIG. 3B shows concentric nested cams 340 withdifferent incline angles, according to an example embodiment. Morespecifically, an outer cam 342 may have a lowest point 344 that rises toa highest point 346 at a certain angle of incline. Additionally, aninner cam 348 nested inside the outer cam 342 may have a lowest point350 that rises to a highest point 352 at a steeper angle of incline. Byusing different incline angles, an actuator may be designed with camsthat rotate within different ranges of rotational motion.

In additional examples, one or both of the outer cam and the inner cammay have non-constant incline angles. By using a non-constant inclineangle, the transmission ratio may be varied based on the local angle ofthe helix at which a roller is located. For instance, FIG. 3C showsconcentric nested cams 360 with non-constant incline angles, accordingto an example embodiment. More specifically, an outer cam 362 may have alowest point 364 that rises to a highest point 366 at a non-constantangle, such that the surface of the outer cam 362 has one or moreundulations 378. Additionally, an inner cam 368 nested inside outer cam362 may rise from a lowest point 364 to a highest point 366, such asthat the inner cam 368 has one or more undulations 380.

By using cam surfaces with non-constant incline angles, differenttransmission ratios may be achieved at different points of motion. Insome examples, a robot part may therefore be created with non-constantjoint strength. For instance, at some points of rotational motion, thejoint may be made to rotate faster (but weaker), while at other pointsof rotational motion, the joint may be made to rotate slower (butstronger). The incline angles of the inner cam and outer cam may bevaried in other ways as well.

FIG. 4 shows a robotic arm, according to an example embodiment. Morespecifically, an example robotic device (such as robotic device 100 inrelation to FIG. 1) may include a robot arm 400 equipped with severallinear-to-rotary actuators 402, 404, 406. The actuators may becontrolled by a control system (e.g., a microprocessor, FPGA,microcontroller, or the like) of the robot to separately rotatedifferent joints of the robot arm 400. For instance, the actuators maybe used to rotate particular joints to perform functions or to interactwith the environment.

In order to use an actuator to produce rotational motion of the joint,the joint may be coupled to a rotational component of one of theactuators. As an example, the outer cam of one of the actuators may becoupled to a robotic arm joint, and the inner cam of the actuator may befixed from rotation. Accordingly, linear actuation of one of the pistonsof the actuator may cause the outer cam to rotate within a range ofmotion close to 360 degrees, thereby allowing the robotic arm joint torotate within a range of motion close to 360 degrees.

Different numbers and placements of linear-to-rotary actuators within arobotic device are also possible. In some examples, one or more of theactuators may include pistons with the same diameter to create jointswith symmetric joint strength (e.g., the same torque in bothdirections). In other examples, one or more of the actuators used forcertain joints may include an outer ramp and an inner ramp withnon-constant incline angles (e.g., undulating sweeps) to create jointswith non-constant joint strength. In additional examples, unbalancedactuators containing pistons with different diameters may be used tocreate joints with asymmetric joint strength (e.g., more torque in onedirection than the other). Other combinations are also possible.

FIG. 5 illustrates a computer-readable medium configured according to anexample embodiment. In example embodiments, an example robotic devicecan include one or more processors, one or more forms of memory, one ormore input devices/interfaces, one or more output devices/interfaces,and machine-readable instructions that when executed by the one or moreprocessors cause the system to carry out the various functions, tasks,capabilities, etc., described above.

In some embodiments, example functions or methods may be implemented bycomputer program instructions encoded on a non-transitorycomputer-readable storage media in a machine-readable format, or onother non-transitory media or articles of manufacture. FIG. 5 is aschematic illustrating a conceptual partial view of an example computerprogram product that includes a computer program for executing acomputer process on a computing device, arranged according to at leastsome embodiments presented herein.

In one embodiment, the example computer program product 500 is providedusing a signal bearing medium 502. The signal bearing medium 502 mayinclude one or more programming instructions 504 that, when executed byone or more processors may provide functionality or portions of thefunctionality described above with respect to FIGS. 1, 2A-2C, 3A-3C,and/or 4. In some examples, the signal bearing medium 502 can be acomputer-readable medium 506, such as, but not limited to, a hard diskdrive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape,memory, etc. In some implementations, the signal bearing medium 502 canbe a computer recordable medium 508, such as, but not limited to,memory, read/write (R/W) CDs, R/W DVDs, etc. In some implementations,the signal bearing medium 502 can be a communications medium 510, suchas, but not limited to, a digital and/or an analog communication medium(e.g., a fiber optic cable, a waveguide, a wired communications link, awireless communication link, etc.). Thus, for example, the signalbearing medium 502 can be conveyed by a wireless form of thecommunications medium 510.

The one or more programming instructions 504 can be, for example,computer executable and/or logic implemented instructions. In someexamples, a computing device such as the processor 118 of FIG. 1 isconfigured to provide various operations, functions, or actions inresponse to the programming instructions 504 conveyed to the processor118 by one or more of the computer-readable medium 506, the computerrecordable medium 508, and/or the communications medium 510.

The non-transitory computer-readable medium 508 could also bedistributed among multiple data storage elements, which could beremotely located from each other. The device that executes some or allof the stored instructions could be a client-side computing device.Alternatively, the device that executes some or all of the storedinstructions could be a server-side computing device.

Within some examples herein, operations may be described as methods forperforming functions, and methods may be embodied on a computer programproduct (e.g., a tangible computer readable storage medium ornon-transitory computer readable medium) that includes instructionsexecutable to perform the functions.

FIG. 6 is a flowchart illustrating an example method 600 for operating arobotic device. The method 600 may be embodied as computer executableinstructions stored on non-transitory media, such as the configurationdescribed above in relation to FIG. 5, for example.

At block 602, the method 600 may include determining a groundedcomponent from a group of three components including a circular outerincline ramp, a circular inner incline ramp, and a piston carrier. Morespecifically, the three components may be arranged such as illustratedand described with respect to FIGS. 2A-2C, FIGS. 3A-3C, and/or FIG. 4.One component from the group may be chosen as the ground to enablerotation of the remaining two components about a central axis. Forinstance, in order to produce a gearing effect to achieve an extendrange of rotational motion, either the inner cam or the outer cam may bechosen as the ground. To cause the two end cams to rotate in oppositedirections, the piston carrier may instead be chosen as the groundedcomponent.

At block 604, the method 600 may also include causing the groundedcomponent to become fixed from rotation about the central axis. Forinstance, a device may include one or more separate actuators thatfunction to prevent rotation of one or more of the outer cam, the innercam, and the piston carrier. Once a component to serve as the ground isselected, a corresponding actuator may be activated to stop the groundedcomponent from rotating. In some examples, the grounded component may bechanged at one or more points in time as well, depending on desiredoutput from the actuator.

At block 606, the method 600 may further include driving first piston ofthe piston carrier toward the circular outer incline ramp and thecircular inner incline ramp. More specifically, a control system mayselect which of the two pistons to activate depending on which directionof rotation is desired for the ungrounded components. A roller of thepiston may act on the two end cams, producing rotations of the twoungrounded components, and also forcing the second piston in a directionaway from the two end cams. In some examples, the method may furtherinclude driving the second piston toward the end cams at a future pointin time to cause the two ungrounded components to rotate in oppositedirections.

It should be understood that arrangements described herein are forpurposes of example only. As such, those skilled in the art willappreciate that other arrangements and other elements (e.g. machines,interfaces, functions, orders, and groupings of functions, etc.) can beused instead, and some elements may be omitted altogether according tothe desired results. Further, many of the elements that are describedare functional entities that may be implemented as discrete ordistributed components or in conjunction with other components, in anysuitable combination and location, or other structural elementsdescribed as independent structures may be combined.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopebeing indicated by the following claims, along with the full scope ofequivalents to which such claims are entitled. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting.

What is claimed is:
 1. A method comprising: determining a groundedcomponent from a group of three components to enable rotation of twoungrounded components from the group about a central axis, wherein thegroup comprises (1) a rounded outer incline ramp surrounding the centralaxis, (2) a rounded inner incline ramp surrounding the central axis andinversely aligned from the rounded outer incline ramp, and (3) a pistoncarrier oriented in a direction parallel to the central axis; causingthe grounded component to become fixed from rotation about the centralaxis; and driving a first piston of the piston carrier toward therounded outer incline ramp and the rounded inner incline ramp to producerotations of the two ungrounded components and to force a second pistonfrom the piston carrier in a direction away from the rounded outerincline ramp and the rounded inner incline ramp.
 2. The method of claim1, further comprising driving the second piston of the piston carriertoward the rounded outer incline ramp and the rounded inner incline rampto produce opposite rotations of the two ungrounded components and toforce the first piston in a direction away from the rounded outerincline ramp and the rounded inner incline ramp.
 3. The method of claim1, wherein the first piston comprises a first roller positioned on therounded outer incline ramp and the rounded inner incline ramp at a firstpoint, and wherein the second piston comprises a second rollerpositioned on the rounded outer incline ramp and the rounded innerincline ramp at a second point opposite the first point.
 4. The methodof claim 3, wherein the first point comprises a point at which surfacesof the rounded outer incline ramp and the rounded inner incline ramphave a same height orthogonal to the central axis.
 5. The method ofclaim 3, wherein the first roller comprises a first outer rollerpositioned along the rounded outer incline ramp and a first inner rollerpositioned along the rounded inner incline ramp such that the firstouter roller and the first inner roller are configured to rollindependently of each other.
 6. The method of claim 1, wherein each ofthe rounded outer incline ramp and the rounded inner incline rampcomprises a first semicircular portion extending from a lowest point toa highest point and a second semicircular portion opposite the firstsemicircular portion.
 7. The method of claim 1, wherein the roundedouter incline ramp and the rounded inner incline ramp have a same pitch.8. The method of claim 1, wherein the rounded inner incline ramp isfixed from rotation such that a linear motion of the first piston towardthe rounded outer incline ramp and the rounded inner incline ramp causesa rotation of the piston carrier and the rounded outer incline ramp. 9.The method of claim 8, wherein the rounded outer incline ramp and therounded inner incline ramp have a same pitch such that the linear motionof the first piston toward the rounded outer incline ramp and therounded inner incline ramp causes the rounded outer incline ramp torotate twice as fast as the piston carrier.
 10. The method of claim 1,wherein the piston carrier is fixed from rotation such that a linearmotion by the first piston toward the rounded outer incline ramp and therounded inner incline ramp causes a rotation of the rounded innerincline ramp and the rounded outer incline ramp in opposite directions.11. The method of claim 10, wherein the rounded outer incline ramp andthe rounded inner incline ramp have a same pitch such that the linearmotion of the first piston toward the rounded outer incline ramp and therounded inner incline ramp causes the rounded outer incline ramp torotate at a same speed as the rounded inner incline ramp.
 12. The methodof claim 10 wherein the rounded outer incline ramp and the rounded innerincline ramp have a different pitch such that the linear motion of thefirst piston toward the rounded outer incline ramp and the rounded innerincline ramp causes the rounded outer incline ramp to rotate at adifferent speed than the rounded inner incline ramp.
 13. The method ofclaim 1, wherein at least one of the rounded outer incline ramp and therounded inner incline ramp has a non-constant incline angle such that alinear motion of the first piston toward the rounded outer incline rampand the rounded inner incline ramp causes a rotation of at least one ofthe rounded outer incline ramp and the rounded inner incline ramp withnon-constant speed.
 14. The method of claim 13, wherein the at least oneof the rounded outer incline ramp and the rounded inner incline rampthat has the non-constant incline angle comprises a surface with aplurality of undulations.
 15. The method of claim 1, wherein causing thegrounded component to become fixed from rotation about the central axiscomprises activating an actuator corresponding to the grounded componentto prevent rotation of the grounded component.
 16. A non-transitorycomputer readable medium having stored therein instructions, that whenexecuted by a computing system, cause the computing system to performfunctions comprising: determining a grounded component from a group ofthree components to enable rotation of two ungrounded components fromthe group about a central axis, wherein the group comprises (1) arounded outer incline ramp surrounding the central axis, (2) a roundedinner incline ramp surrounding the central axis and inversely alignedfrom the rounded outer incline ramp, and (3) a piston carrier orientedin a direction parallel to the central axis; causing the groundedcomponent to become fixed from rotation about the central axis; anddriving a first piston of the piston carrier toward the rounded outerincline ramp and the rounded inner incline ramp to produce rotations ofthe two ungrounded components and to force a second piston from thepiston carrier in a direction away from the rounded outer incline rampand the rounded inner incline ramp.
 17. The non-transitory computerreadable medium of claim 16, wherein the functions further comprisedriving the second piston of the piston carrier toward the rounded outerincline ramp and the rounded inner incline ramp to produce oppositerotations of the two ungrounded components and to force the first pistonin a direction away from the rounded outer incline ramp and the roundedinner incline ramp.
 18. The non-transitory computer readable medium ofclaim 16, wherein the first piston comprises a first roller positionedon the rounded outer incline ramp and the rounded inner incline ramp ata first point, and wherein the second piston comprises a second rollerpositioned on the rounded outer incline ramp and the rounded innerincline ramp at a second point opposite the first point.
 19. A systemcomprising: at least one processor; and a non-transitory computerreadable medium having stored therein instructions, that when executedby the at least on processor, cause the at least one processor toperform functions comprising: determining a grounded component from agroup of three components to enable rotation of two ungroundedcomponents from the group about a central axis, wherein the groupcomprises (1) a rounded outer incline ramp surrounding the central axis,(2) a rounded inner incline ramp surrounding the central axis andinversely aligned from the rounded outer incline ramp, and (3) a pistoncarrier oriented in a direction parallel to the central axis; causingthe grounded component to become fixed from rotation about the centralaxis; and driving a first piston of the piston carrier toward therounded outer incline ramp and the rounded inner incline ramp to producerotations of the two ungrounded components and to force a second pistonfrom the piston carrier in a direction away from the rounded outerincline ramp and the rounded inner incline ramp.
 20. The system of claim19, wherein the first piston comprises a first roller positioned on therounded outer incline ramp and the rounded inner incline ramp at a firstpoint, and wherein the second piston comprises a second rollerpositioned on the rounded outer incline ramp and the rounded innerincline ramp at a second point opposite the first point.